Mass spectrometer beam regulator



Sept- 1953 w. R. BAKER 2,651,723

MASS SPECTROMETER BEAM REGULATOR Filed June 1946 x o- --o 0 TO COLLECTING MODULATED RECENER AND POCKET R.F. OSCILLATOR V DEMODULATOR.

l 4 TD ACCELERATING REGULATED ELECTRODE |-|.v. SUPPLY INVENTOR WILLIAM R. BAKER BY a M Patented Sept. 8, 1953 MASS SPECTROMETER BEAM REGULATOR William R. Baker, Berkeley, Calif., assignor to the United States of America as represented by the United States Atomic Energy Commission Application June 28, 1946, Serial No. 679,953

4 Claims. 1

This invention relates to a mass spectrometer beam regulator.

An object of this invention is to provide an apparatus for maintaining a constant current to a mass spectrometer beam collector where there is a large difference of potential between the collector and the mass spectrometer beam accelerating electrode.

Other and further objects of this invention will be apparent to those skilled in the art to which it relates from the following specification, claims and drawing.

In a mass spectrometer beam regulator it is often desirable to introduce the regulating Voltage into the high voltage side of the accelerating electrode power supply in order to reduce possibility of interference with the high voltage regulator of said power supply. This may in general be accomplished by modulating a radio frequency oscillator as a function of the collected beam current, and transmitting the current so produced to a demodulatin network which is positioned at the high voltage side of the accelerating voltage supply. The accelerating voltage is thence regulated by the output of the demodulating network.

Referring to the drawing briefly, the sole figure thereof is a schematic wiring diagram of an embodiment of this invention.

Referring to the drawing in detail, reference numeral IE! designates the terminals of this apparatus connected to the beam receiver of a mass spectrometer. These terminals ID are connected to the input of the modulated radio frequency oscillator II and the currents received by the terminals I6 function to modulate the radio frequency oscillations generated by the apparatus H. The output of this apparatus 1 I is connected to the primary of the radio frequency transformer l2, the secondary of which is connected to the apparatus I3 which comprises a radio receiving circuit including suitable amplifiers and a suitable demodulator for converting the modulated radio frequency into pulsating direct current. This pulsating direct current is applied across the resistor section l5 of the voltage divider resistor I4 so that apparatus l3 operates to insert into the regulated high voltage applied across the voltage divider M from the regulated high voltage supply l8, an incremental voltage proportional to the current received by the mass spectrometer collector connected to the terminals Ill. The terminals [6 and ll of the voltage divider M are connected to the accelerating electrode structure of the mass spectrometer for exp-- plying a potential between the accelerator electrode and the ion source.

As an example of operation consider the instance where it is desired to regulate a mass spectrometer to identify an element in the presence of large quantities of another element of slightly greater mass. In this case the beam current received by the collector may directly amplitude-modulate the radio frequency oscillator H which transmits a signal through the radio frequency transformer l2 which is loosely coupled and well insulated for high voltage. This signal is received by the receiver l3 and demodulated and the output of this receiver is applied across resistor section 15 in phase with the voltage of the regulated high voltage supply H). An increase in collector current thus increases the voltage output of receiver [3 which is added to the voltage of supply [8 to increase the accelerating voltage and return the mass spectrometer beam to normal position. A decrease in collector current produces a corresponding decrease in the accelerating voltage and thus the invention operates to regulate the high voltage applied to the accelerator electrode of the mass spectrometer and to maintain the beam in a desired position on the mass spectrometer collecting electrode. It

will be appreciated that the above-noted operation is highly advantageous when the mass spectrometer is employed to separate one element from a conglomerate source material and particularly when the mass of such element is nearly the same as the mass of another element present in greater quantity; as in this circumstance regulation about a point on the sloping mass v. intensity curve of the more abundant element is required.

While I have described the salient features of this invention in detail with respect to one embodiment and have suggested one use of a mass spectrometer in which the present invention is particularly advantageous, it will of course be apparent that numerous modifications may be made within the spirit and scope of this invention and I do not therefore desire to limit the invention to the exact details shown except in so far as they may be defined in the following claims.

What is claimed is:

1. In a mass spectrometer beam regulator, a radio frequency oscillator, means for modulating said oscillator as a function of the collected beam current and means controlled by the output of said oscillator for regulating the mass spectrometer beam.

2. A mass spectrometer beam regulator as set forth in claim 1 further characterized in that the last means consists of a regulated high voltage supply connected to the accelerator electrode of a mass spectrometer.

3. In a mass spectrometer beam regulator, a radio frequency oscillator, connections for connecting said radio frequency oscillator to the collector of the mass spectrometer whereby the radio frequency generated by said oscillator is modulated in accordance with the current collected by said collector, a radio frequency transformer connected to the output of said oscillator, a receiver and demodulator connected to the output of said radio frequency transformer, a high voltage supply, a voltage divider connected across said high voltage supply, connections for connecting said voltage divider to the accelerator electrode of said mass spectrometer, a tap on said voltage divider, said tap being connected to said demodulator whereby the said demodulator insertsa voltage increment across said tapped voltage divider to shift said mass spectrometer beam in accordance with variations in the current collected by said collector.

4. An ion beam regulator comprising a radio frequency oscillator, a modulator having input terminals adapted for connection to the ion col-- lector of a mass spectrometer and responsive to the ion current thereto, said modulator being connected to said radio frequency oscillator for modulating the radio frequency output voltage thereof, a radio frequency receiver and demodulator, a radio frequency transformer coupling said radio frequency generator to said radio frequency receiver and demodulator whereby the output of said demodulator corresponds to the output of said modulator, a high voltage source, a voltage divider connected in shunt across said high voltage source, and electrical connections between said demodulator output and said voltage divider for impressing said demodulator output voltage across a portion 01 said voltage divider, said voltage divider having end terminals adapted for connection to the accelerating electrodes of a mass spectrometer to regulate the voltage thereof in accordance with the magnitude of the ion current to said modulator.

WILLIAM R. BAKER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,331,189 Hipplc Oct. 5, 1943 

